The subject matter disclosed herein relates to a control circuit for enabling an aerial lift member. Specifically, a control circuit for enabling an aerial lift member including an interlock portion and an over ride of the interlock portion including a self-disabling over-ride switch is disclosed.
As is known to those skilled in the art, some mobile vehicles have an auxiliary member which may be extended away from the main body portion of the vehicle. For example, aerial lift trucks may include a boom that can be extended upward and can be rotated up to a continuous 360 degrees of rotation; fire trucks may include an extension ladder that, similarly, may be extended upward and rotated about the vehicle; and construction equipment may include a digging member extending away from the front or rear of the vehicle. In each example, the center of gravity of the vehicle changes as the auxiliary member is extended away from or rotated around the vehicle, creating a potential for the vehicle to tip over.
Stabilizing members are typically provided on those mobile vehicles having an auxiliary member to prevent the vehicle from tipping over while the auxiliary member is in operation. Such stabilizing members, also known as outriggers, may be extended and retracted. In the retracted position, the stabilizing member is stored, typically adjacent to the body of the vehicle, such that the stabilizing member does not interfere with the mobility of the vehicle. In the extended position, the stabilizing member is positioned away from the body of the vehicle such that the stabilizer pad engages the ground, or other solid surface, to stabilize the vehicle when the auxiliary member is in operation.
An interlock, preventing activation of the auxiliary member, is typically provided in order to ensure that the stabilizing members are extended prior to operating the auxiliary member. Typically, the auxiliary member is manually enabled and disabled by an operator, for example by a switch, lever, or push-button. Enabling the auxiliary member engages actuators, such as relays, solenoids, or valves to provide electrical or hydraulic power, as required by the auxiliary member, and permits motion of the auxiliary member. In order to determine whether the stabilizing members are extended, each stabilizing member has a sensor or a switch associated with that stabilizing member indicating whether the stabilizing member is extended. The sensor or switch interlocks activation of the auxiliary member such that it may not be enabled until each of the stabilizing members is fully extended and engaging the ground.
However, such an interlock presents potential disadvantages. For example, the mobile vehicle may be parked on a sloped surface or next to a curb on a street. On such surfaces, the stabilizing member may engage the ground yet not be fully extended. Consequently, the sensor on the stabilizing member indicates that stabilizing member is not fully extended and prevents the auxiliary member from operating. Alternately, one of the sensors or stabilizing members may fail and similarly prevent the sensor from indicating that the stabilizing members are extended. As still another example, the mobile vehicle may be in a garage for service. The auxiliary member may need to be operated while in the garage but there may be no room to extend the stabilizing member. In each example, an operator could determine that the auxiliary member is safe to operate but, nevertheless, be prevented from operating the auxiliary member by the interlock.
In an attempt to overcome this disadvantage, some mobile vehicles provide an over ride for the interlock system, permitting the operator to determine whether the auxiliary member is safe to operate. However, such over rides are typically a maintained style of switch, such as a toggle or selector switch that remains active until the switch is returned to its previous state. Such an over ride switch may inadvertently be left on by the operator after the operation of the auxiliary member is complete, causing an interlock from the stabilizing members to be ignored the next time the auxiliary member is in use. Alternately, if vehicles are not equipped with an over ride, the operator may install a jumper, or a wire, around the interlock portion of the control in order to permit operation of the auxiliary member. Again, the jumper may inadvertently be left on after operating the auxiliary member, causing the interlock of the stabilizing members to be bypassed at the next operation of the auxiliary member.
Therefore, it is desirable to provide an interlock over ride that permits an operator to bypass the interlock during a single operation of the auxiliary member and prevents the bypass from remaining active during subsequent operations of the auxiliary member.